AbstractIn this work, a diketopyrrolopyrrole‐based 2D covalent–organic framework (COF) is realized and featured with broadband optical absorption and high solar‐thermal conversion performance. Moreover, a 3D hierarchical structure, referred to as COF‐based hierarchical structure (COFHS), is rationally designed to achieve an enhanced photothermal conversion efficiency. In this water evaporator, diketopyrrolopyrrole is immobilized into conjugated COF to achieve enhanced light absorption, whereas a porous PVA network scaffold is utilized to support COF sheets as well as to enhance the hydrophilicity of the evaporator. Due to this structural advantage, COFHS displays a high solar‐to‐vapor energy conversion efficiency of 93.2%. Under 1 sun AM1.5 G irradiation, a stable water evaporation rate of 2.5 kg m^–2 h^–1 can be achieved. As a proof‐of‐concept application, a water collection device prepared with the COFHS can achieve high solar‐thermal water collection efficiency of 10.2 L m^–2 d^–1 under natural solar irradiation. The good solar‐thermal conversion properties and high‐water evaporation rate make the COFHS a promising platform for solar‐thermal water production.